TCP/IP Protocol Suite 1 Chapter 19 Upon completion you will be able to: File Transfer: FTP and TFTP Understand the connections needed for FTP file transfer Be familiar with FTP commands and responses Know the differences between FTP and TFTP Be familiar with TFTP message types Understand TFTP flow and error control Objectives

TCP/IP Protocol Suite FILE TRANSFER PROTOCOL (FTP) File Transfer Protocol (FTP) is the standard mechanism provided by TCP/IP for copying a file from one host to another. The topics discussed in this section include: ConnectionsCommunication Command Processing File Transfer Anonymous FTP

TCP/IP Protocol Suite 3 FTP uses the services of TCP. It needs two TCP connections. The well-known port 21 is used for the control connection and the well- known port 20 for the data connection. Note:

TCP/IP Protocol Suite 4 Figure 19.1 FTP

TCP/IP Protocol Suite 5 Figure 19.2 Opening the control connection

TCP/IP Protocol Suite 6 Figure 19.3 Creating the data connection

TCP/IP Protocol Suite 7 Figure 19.4 Using the control connection

TCP/IP Protocol Suite 8 Figure 19.5 Using the data connection

TCP/IP Protocol Suite 9 Figure 19.6 Command processing

TCP/IP Protocol Suite 10 Table 19.1 Access commands

TCP/IP Protocol Suite 11 Table 19.2 File management commands

TCP/IP Protocol Suite 12 Table 19.3 Data formatting commands

TCP/IP Protocol Suite 13 Table 19.4 Port defining commands

TCP/IP Protocol Suite 14 Table 19.5 File transfer commands

TCP/IP Protocol Suite 15 Table 19.5 File transfer commands (continued)

TCP/IP Protocol Suite 16 Table 19.6 Miscellaneous commands

TCP/IP Protocol Suite 17 Table 19.7 Responses

TCP/IP Protocol Suite 18 Table 19.7 Responses (continued)

TCP/IP Protocol Suite 19 Table 19.7 Responses (continued)

TCP/IP Protocol Suite 20 Table 19.7 Responses (continued)

TCP/IP Protocol Suite 21 Table 19.7 Responses (continued)

TCP/IP Protocol Suite 22 Figure 19.7 File transfer

TCP/IP Protocol Suite 23 Figure 19.8 shows an example of using FTP for retrieving a list of items in a directory. 1. After the control connection to port 21 is created, the FTP server sends the 220 (service ready) response on the control connection. 2. The client sends the USER command. 3. The server responds with 331 (user name is OK, password is required). 4. The client sends the PASS command. 5. The server responds with 230 (user login is OK) Example 1 See Next Slide

TCP/IP Protocol Suite The client issues a passive open on an ephemeral port for the data connection and sends the PORT command (over the control connection) to give this port number to the server. 7. The server does not open the connection at this time, but it prepares itself for issuing an active open on the data connection between port 20 (server side) and the ephemeral port received from the client. It sends response 150 (data connection will open shortly). 8. The client sends the LIST message. 9. Now the server responds with 125 and opens the data connection. Example 1 (cONTINUED) See Next Slide

TCP/IP Protocol Suite The server then sends the list of the files or directories (as a file) on the data connection. When the whole list (file) is sent, the server responds with 226 (closing data connection) over the control connection. 11. The client now has two choices. It can use the QUIT command to request the closing of the control connection or it can send another command to start another activity (and eventually open another data connection). In our example, the client sends a QUIT command. 12. After receiving the QUIT command, the server responds with 221 (service closing) and then closes the control connection. Example 1 (cONTINUED) See Next Slide

TCP/IP Protocol Suite 26 Figure 19.8 Example 1

TCP/IP Protocol Suite 27 The following shows an actual FTP session that parallels Example 1. The colored lines show the responses from the server control connection; the black lines show the commands sent by the client. The lines in white with black background shows data transfer. Example 2 See Next Slide $ ftp voyager.deanza.fhda.edu Connected to voyager.deanza.fhda.edu. 220 (vsFTPd 1.2.1) 530 Please login with USER and PASS. Name (voyager.deanza.fhda.edu:forouzan): forouzan 331 Please specify the password.

TCP/IP Protocol Suite 28 Example 2 Password: 230 Login successful. Remote system type is UNIX. Using binary mode to transfer files. ftp> ls reports 227 Entering Passive Mode (153,18,17,11,238,169) 150 Here comes the directory listing. drwxr-xr-x Sep business drwxr-xr-x Sep personal drwxr-xr-x Sep school 226 Directory send OK. ftp> quit 221 Goodbye.

TCP/IP Protocol Suite 29 Figure 19.9 shows an example of how an image (binary) file is stored. 1. After the control connection to port 21 is created, the FTP server sends the 220 (service ready) response on the control connection. 2. The client sends the USER command. 3. The server responds with 331 (user name is OK, a password is required). 4. The client sends the PASS command. 5. The server responds with 230 (user login is OK). 6. The client issues a passive open on an ephemeral port for the data connection and sends the PORT command (over the control connection) to give this port number to the server. Example 3 See Next Slide

TCP/IP Protocol Suite The server does not open the connection at this time, but prepares itself for issuing an active open on the data connection between port 20 (server side) and the ephemeral port received from the client. It sends the response 150 (data connection will open shortly). 8. The client sends the TYPE command. 9. The server responds with the response 200 (command OK). 10. The client sends the STRU command. 11. The server responds with 200 (command OK). 12. The client sends the STOR command. 13. The server opens the data connection and sends the response 250. Example 3 (cONTINUED) See Next Slide

TCP/IP Protocol Suite The client sends the file on the data connection. After the entire file is sent, the data connection is closed. Closing the data connection means end-of-file. 15. The server sends the response 226 on the control connection. 16. The client sends the QUIT command or uses other commands to open another data connection for transferring another file. In our example, the QUIT command is sent. 17. The server responds with 221 (service closing) and it closes the control connection. Example 3 (cONTINUED) See Next Slide

TCP/IP Protocol Suite 32 Figure 19.9 Example 3

TCP/IP Protocol Suite 33 We show an example of anonymous FTP. We assume that some public data are available at internic.net. Example 4 See Next Slide $ ftp internic.net Connected to internic.net 220 Server ready Name: anonymous 331 Guest login OK, send “guest” as password Password: guest ftp > pwd 257 ’/’ is current directory

TCP/IP Protocol Suite 34 bin Example 4 ftp > close 221 Goodbye ftp > quit

TCP/IP Protocol Suite TRIVIAL FILE TRANSFER PROTOCOL (TFTP) Trivial File Transfer Protocol (TFTP) is a simple file transfer protocol without the sophisticated features of FTP. The topics discussed in this section include: MessagesConnection Data Transfer UDP Ports TFTP Example TFTP Options SecurityApplications

TCP/IP Protocol Suite 36 TFTP uses the services of UDP on the well-known port 69. Note:

TCP/IP Protocol Suite 37 Figure Message categories

TCP/IP Protocol Suite 38 Figure RRQ format

TCP/IP Protocol Suite 39 Figure WRQ format

TCP/IP Protocol Suite 40 Figure DATA format

TCP/IP Protocol Suite 41 Figure ACK format

TCP/IP Protocol Suite 42 Figure ERROR format

TCP/IP Protocol Suite 43 Table 19.8 Error numbers and their meanings

TCP/IP Protocol Suite 44 Figure Connection establishment

TCP/IP Protocol Suite 45 Figure Sorcerer’s apprentice bug

TCP/IP Protocol Suite 46 Figure UDP port numbers used by TFTP

TCP/IP Protocol Suite 47 Figure TFTP example

TCP/IP Protocol Suite 48 Figure Use of TFTP with BOOTP